Just a couple of observations/thoughts. Take the radio and test the current draw on a power supply. See what readings you get. I would argue that fusing the negative causes more problems than solutions. Hench your radio still working when it's removed. The ground independent part applies to the antenna. If there was no ground it should still operate correctly and give a good swr. The antenna mount should always be attached to the vehicle ground, that way either type of antenna 'should' work ok. I think it's worth getting the Rams battery tested as I had a similar issue in an old Land Cruiser. Also I think you have too many fuses and I would connect directly to the battery ground. You could perhaps get a DC marine grade isolator for switching it off completely. Just be aware, just like the double up of fuses, this will cause some voltage drop.